Project Summary: A phenotypic capacitor buffers the developmental phenotype against genotypic or environmental variation. Under normal conditions, this buffering results in a robust phenotype;however, when challenged by a harsh environment or mutation, the capacitor may fail, thereby revealing the variation phenotypically. This activity provides for both a mechanism by which hidden polymorphism can accumulate and, by failure of the phenotypic capacitor, a mechanism by which evolutionary change can be promoted. The primary example of a phenotypic capacitor is Hsp90, a molecular chaperone that normally suppresses phenotypic variation but releases this variation when functionally compromised, resulting in pleiotropic phenotypic effects. While only Hsp90 has been shown to act as a phenotypic capacitor of both genotypic and environmental variation, several experimental and computational studies suggest Hsp90 may not be unique in this role. In this study, I will test the hypothesis that multiple gene products are capable of acting as phenotypic capacitors of environmental and genotypic variation. In the preliminary results, I have analyzed existing quantitative morphological data from 4718 Saccharomyces cerevisiae single-gene deletion strains for high overall phenotypic variance and identified multiple putative capacitors of environmental variation. Aim 1. To test the hypothesis that gene products capable of acting as phenotypic capacitors of environmental variation also act as capacitors of genotypic variation, lab yeast strains with deletions in genes that code for putative environmental capacitors will be crossed with a wild isolate strain to generate genetic variation. The phenotypic variability of deletion-containing and wild-type F1 haploid segregants will be compared using an array of quantitative phenotypic assays. Aim 2. To identify quantitative trait loci that may act as phenotypic capacitors, linkage analysis for high and low phenotypic variance will be performed on existing genotyped lines of a cross between a genetically divergent lab strain and wild isolate. The identification and characterization of novel phenotypic capacitors will enhance the understanding of phenotypic robustness, cancer cell progression, and the mechanisms for evolutionary change of organisms including microbial pathogens. Relevance: I plan to identify key genes that affect the rate of evolutionary change. Many human pathogens evolve rapidly to avoid the immune response or antibiotics. This study will help understand the mechanisms and genes behind this evolution. Additionally, cancer cells go through a form of evolution from being normal cells to becoming malignant. Thus, genes identified here are likely to be important to understanding how cancer progresses and may be treated.